Many industrial processes utilize large quantities of water which become contaminated with toxic organic wastes. Water carrying some contaminants, such as pesticides, at parts per million or even parts per billion levels might pose a threat to the public health and/or environment if discharged without purification. The need exists for new and better methods to remove substantially hazardous substances from water so that the water may be reused or discharged into the environment.
A known method for removing organic contaminants from water is by contacting the stream of process water with a countercurrent stream of an immiscible organic solvent in which the contaminant is more soluble than in water. Due to the expense of the organic solvent, it is important to recover it from the extract so that it may be recycled into the extraction process. A usual consequence of liquid-liquid extraction is that, due to the slight but consequential solubility of the solvent in water, the solvent itself contaminates the water and must be removed.
Prior art extraction processes have employed methods of removing the solvent from the extract and/or raffinate which require significant input of thermal energy. U.S. Pat. No. 4,162,902 describes the use of steam-stripping to vaporize the solvent from the extracted phenol. Solvents may be removed from the raffinate by steam-stripping, such as is described in U.S. Pat. No. 3,449,244 or by distillation, such as is described in U.S. Pat. No. 3,247,143. It would be desirable to have more energy-efficient methods of purifying process water.
Accordingly, it is a primary object of the present invention to provide contaminant-extraction processes which substantially remove organic contaminants from process water and recycle the solvent with minimal expenditure of thermal energy.